Molding machine



2 Sheets-Sheet l INVENTOR 4 mmmx :2252;:

J. J. BURNS MOLDING MACHINE Filed July 25;

Nov. 14, 1933.

Nov. 14, 1933. J. J, BURNS 1,935,076

MOLDING MACHINE Filed July 25, 1929 l 2 sheets-sheet. 2

4 27 Z7 i 'I Z// 21 1 p g 35 g 37 lill IN NNNNNN OR Patented ,Noya 14, 1933 y* y l UNITED STAT-Es lPATENT ,OFFICE Application July 25, 19.29.k Serial Nol 380,855 3 Claims. (Cl. 535-15) My invention relates to molding machines, and adhere to the flexible covering to yany way near more'particularly to pistons or plungers for workas great an extent as upon the withdrawalof a ing earthy materials. rigid metallic piston. As a result, the piston is In working earthy materials, such as clay and withdrawn from engagement with` the material the like, in molding operations, the earthy'main the cylinder without vibrations such as are-60 terialV is often forced through a shaping die at the caused by the tearing away of a rigid metallic end of a cylinder underv considerable pressure piston from engagement with a body of earthy applied by a piston or plunger. The pressure material. Also, the continuity ofthe material compacts the earthy material to a substantially in the cylinder is not disturbed to such an extent l uniform consistency and tends to exclude any as to form large bubbles or pockets which after- 65 air and to close any air pockets which might be wards produce defective articles.

in the material. vThe accompanying drawings illustratecertain The characteristics of the adhesion between the preferred embodiments of the invention, in which surface of a rigid metallic piston and a mass of yFigure 1 is a sectional View of a portion of a 'lo earthy material are such that upon the withmolding machine embodying myinvention; land 70y drawal of the piston at the end of a molding stroke Figures 2, 3, and 4 are cross-sectional views of a large part of the adjacent compacted earthy modied forms of pistons. material is torn from the mass of material com- Referring to Fig. l, `a molding machine for municating with the die in the cooperating cyl- Vearthy materials comprises a cylinder 2, in which inder. The material adhering to the piston often a piston rod 4 and piston 5 threaded thereon 75 extends over a largeportion of the face of the vreciprocate for forcing'earthy.material through piston and may weigh several pounds. The suca die opening '7 disposed below the Vcylinder 2. tion or condition of partial vacuum existingin A ring section 8 is connected to the bottom of the cylinder at the beginning of the return stroke the `cylinder 2 yby clamping bolts 9. The ring ofv the piston is of some importance incausing section supports a block 10 which directs the 80 the adhesion. movement of the material 6 as it moves from The above described action is disadvantageous thecylinder 2 toward the opening 7. A terminal because it causes a jerking or vibrating of the ring 11 is clamped to the ring section 8 by bolts machine at the instant when the back pressureis 12 and supports a bottom or terminal plate 13 so overcomey and the piston and adhering earthyy by bolts 14. The terminal plate 13 denes the 85 material are separated from the remainder of the outer edges of the die opening 7. As itis well earthy material in the cylinder. The back-pull on understood in the art, the exact shape of the the rmass `of material also breaks the continuity die opening 7 may vary in accordance with the of the material and creates pockets. Upon asub-Y desired Snape of the iinished article. For tiles sequent application 0f pressure 60 the material, the shape of the opening? is frequently circular 90 the pockets are not entirely closed andthe en'-Y in Cross-section, trapped airis apt to form blisters or bubbles The innersurface of the die opening '7 is which produce defective articles- 'Furthermora defined bythe outer surface of a disc 15 Secured the material which hasbeerl disturbed by the by'a bolt 16 to the block li). As is well under- 4o vacuum, or suction action, Whon'subsequentlv Stood in `the art, tnegbloek- 10 is secured to the 95,

brought in contact with new material andA with ring 3 by bracing webs 1'7,

the previously compressed material in the cylin- A Support 13, Carried by 9, phmger 19 'is disder, iS all@ 130 'fOl'm mpeet lIlQS 0f Cleavage, posed below the dieopening'? for receiving shaped due, in part. to the'prosomeof eur pockets material 19 extruded through the die opening 7.

Attempts haVS hele'OfOIe been made t0 TeleVe The piston 5 comprises a metallic disc 21, which 100 the condition of back-pressure or suction by utiis threaded onto the piston rod 4. A clampingy lizing relief valves for admitting air during the ring 24 is provided with a web 25 entering a withdrawal stroke of the piston. However, such seat 26 in the lower surface of the disc 21 to relief valves soon become stopped with earth and which it is secured by a plurality of bolts 2'7. 50. become useless.

I provide a molding machine in which the cominner surface of the cylinder and the router surpressing piston is provided with a flexible coverface of the disc 21. A body 2,8 of flexible maing indirect engagement with the earth being terial is disposed between the lower. part of the compacted and forced through the mold. Upon ring 24 and the web 25 and covers lthe web 26 The ring 24'insures a tight'joint between the 105 I 1 the withdrawal of the piston the earthdoes not and outer surface of the disc 21`for engaging 110 y the earthy material 6. The material 28 is secured by the bolts 27 and by secondary clamping boltsy 29 extending through the body and into the web 26. I have found rubber having a consistency comparable with that used in a tire tread'to be suitable material for the body 28.

When the material 28 is forced into engagement with the earthy material 6, the disc 21 and spacing `ring 24 resist the material, while a heavy pressure of the order of 150 pounds per square inch is applied to the earthy material 6 for forcing it through theV die opening '7. Upon the withdrawal of the piston, the earthy material 6, even when in the form of clay, is released without excessive vibration to the machine and without injuring the continuity of the material remaining in the cylinder by tearing away large masses as is done where a rigid metallic piston is brought into engagement with the earthy material.

While I am not certain of the exact reason for this phenomenon, it -may be causedrby one ora number of different reactions.V It may be ycausedby the flexing action of the material`28 `whenleaving the compacted earthy material by so withdrawing that only small areas of the engaging surfaces of the material and body are separated at vany one time, as distinguished from the lifting of substantially the entire top of the material at one time 'by an inflexible head, such as the metallic pistons heretofore used. Also the characteristics of adhesion between earthy materials,` includingclay, and metallic pistons may be Adifferent than those existing between such earthy materials'and flexible materials. Also it may be that when the material 28 is both flexible and resilient, as in the case of rubber, the material is distorted and compacted during the compression stroke, which action closes the joints existing between the different elements of the piston. Upon the release of the compressing force, the resilient material may tend to return to its normal position before an appreciable amount-of the return stroke takes place. This smallfrestoringl movement of the resilient material may serve, in large part, to break the adhesion between the material 28 and the earthy material 6. The restorative movement of the resilient material may also permit the ini-lltration of a small amount of air for breaking lthe vacuum existing at the beginning of the return stroke. Regardless of the explanation for this phenomenon, I have obtained very satisfactory results by the use `of a live rubber disc or covering-for the end of a piston working against earthy materials. Y

Fig. 2 shows a form of piston in which the disc 21 cooperates with a ring 30 having an overhanging edge 31. In this form of the invention,

` a body of flexible material is cast directly between an overhanging edge 3l on the ring 30 and a web 32, corresponding to the web shown in Fig. 1. In this construction the need for secondary securing bolts, such as bolts 29 in Fig. 1, is eliminated.

Referring to Fig. 3, another form of the invention is illustrated in which a ring 34 having a web 35 is disposed in the seat 26. |The ring 34 is not provided with a downwardly or forwardly extending flange at the edge of a body 36 of flexible material. In this form of the invention, the outer edge 37 of the material 36 directly faces the inner surface of the cylinder 2, and is bolted to the ring 34.

Fig. 4 illustrates a further modification of the invention in which a disc plate 38, having oppositely disposed similar surfaces, is threaded onto the piston rod 4. A covering or diaphragm 39 of flexible material is disposed over the entire outer face 0f the plate 38 by clamping bolts 40 for engagement with earthy material. A reinforcing web or layer 42, in the form of a thinV metal plate is embedded in the body 39 for.

strengthening the latter. This form of the invention is particularly useful for very large pistons. The presence of the web 42 controls the movement of the covering to some extent, but permits sufli cient'ilexibility and/or resiliency to accomplish the Withdrawal of the piston without jerking of machinery or extensive tearing of the adjacent compacted material.

While I have illustrated and described certain present preferred embodiments of the invention, it is to be understood that it may be otherwise embodied Within the spirit of the invention and the scope of the appended claims.

I claim:

l. A-molding machine for plastic material comprising a cylinder having a die opening, a piston for extruding plastic material from said cylinder through said die opening, and a relatively stiiT disc of rubber-like material secured to said pistonfor contact withV said plastic material.

2. A molding? machine `for plastic material comprising a cylinder having a die opening, a piston in 'said cylinder for extruding plastic material from said cylinder through said die opening, a member `of resilient material disposed between said piston and said plastic material, and means securing said member in whole to'said piston.

3. The combination with a chamber lled with plastic material and a member associated therewith for compressing the plastic material, of means including a member of resilient material attached to the surface of said member in contact with the plastic material for permitting the withdrawal of said compression member without creating ak vacuum between saidV compression memberand the plasticl material or effecting the surface of the plastic material in contact with the member of rubber in a manner that Vwould create air pockets between the plastic Ymaterial and a new charge of plastic material under compresirs 

